Field
Aspects of the present invention generally relate to a sheet conveyance device, and an image reading device and an image forming apparatus that include the sheet conveyance device.
Description of the Related Art
A sheet conveyance device applied to an image reading device and an image forming apparatus conveys sheets such as document sheets and recording media separated one by one by a sheet feeding unit. There is proposed a conventional sheet conveyance device that detects double-fed sheets (a plurality of sheets simultaneously fed) which have failed to be separated by a sheet feeding unit, using a double feed detection sensor provided in a conveyance path (refer to U.S. Pat. No. 7,905,484). In general, when double feed is detected using a double feed detection sensor, a user is notified of the double feed so as to be prompted to take out the double-fed sheets.
In a double feed detection unit used in a sheet conveyance device of this type, a transmission-side double feed detection sensor and a reception-side double feed detection sensor are generally disposed to face each other across a conveyance path. In the double feed detection unit, the reception-side double feed detection sensor receives an ultrasonic wave signal transmitted from the transmission-side double feed detection sensor. The double feed detection unit detects the presence or absence of double-fed sheets based on the amplitude change in the received ultrasonic wave.
A conveyance guide for forming the conveyance path is provided with a hole for letting through an ultrasonic wave transmitted and received between the double feed detection sensors. Each double feed detection sensor is disposed in accordance with the position of the hole. The transmission-side double feed detection sensor includes a sensor unit (element) for transmitting an ultrasonic wave and a control circuit board for controlling the sensor. The reception-side double feed detection sensor includes a sensor unit for receiving an ultrasonic wave and a control circuit board for controlling the sensor. The control circuit boards with the respective sensors mounted thereon are each provided with elements for operating the sensor, such as capacitors.
However, in the above-described configuration in which the conveyance guide is provided with a hole at a portion corresponding to the double feed detection sensor, a foreign object such as a staple and a clip accidentally entered the conveyance path may possibly drop through the hole. A foreign object dropped on the control circuit board of the double feed detection sensor may cause malfunction of the control circuit board, such as short-circuit and breakage.
One possible countermeasure for preventing the malfunction caused by a dropped foreign object, such as short-circuit and breakage, is to stick a protection member such as an adhesive tape on the circuit board. However, when an adhesive tape is used, there is a possibility that an adhesive surface may deteriorate over time by the influence of temperature and humidity changes, and the tape may peel off from the control circuit board. Sticking a tape on the control circuit board causes a problem of an increase in the manufacturing cost since it is necessary to ensure a high sticking position accuracy to stick the tape at an accurate position. Therefore, the method for sticking a tape is not an adequate countermeasure.